feat: support environment variables interpolation

[AhmedGrati]

Resolves #21057.

Does this PR introduce a user-facing change?

Adding support to environment variables interpolation in the Kube manifests.

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[rhatdan]

Looks like your tests are failing. I am fine with this, but it does make the YAML file incompatible with Kubernetes, correct?

[AhmedGrati]

@rhatdan considering the following Kubernetes yaml:

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: "2021-08-05T17:55:51Z"
  labels:
    app: foobar
  name: echo_pod
spec:
  containers:
  - command:
    - /bin/sh
    - -c
    - 'echo paren$(FOO) brace${FOO} dollardollarparen$$(FOO) interp$(FOO)olate'
    env:
    - name: PATH
      value: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
    - name: TERM
      value: xterm
    - name: container
      value: podman
    - name: FOO
      value: BAR

The expected behavior is that we should not interpolate and change the command section. So I'm not sure about this PR and if there's any alternative to mitigate this kind of issues. (BTW this is the failing test).

[rhatdan]

@ygalblum PTAL

[ygalblum]

Deciding where to interpolate and where not to will (and has) become as issue. Since K8S doesn't support this, I don't think Podman should.
I've looked at the linked issue (#21057 (comment)) and while there is an oc command that handles it, it is not the create or apply but instead a different command, process, whose output is piped into the former.
So, I think we should close this PR without merging and the issue as won't fix